contactor chattering, replaced it- still have chatter
 

I have a split system (amana condensor RCC36A2E/carrier furnace) and the contactor has started chattering. I replaced the contactor figuring since the old one was pitted that this would fix it, but nope, still chatters. With power to just the thermostat (pulled the outside power), the contactor holds just fine. But once the line power is applied, it will start chattering within a minute.
Have looked over the low voltage line for cuts/nicks/etc, but didn't find anything. Cleaned/scraped and/or replaced the LV connections. Capacitor not bloated.

Can someone offer an idea as to what the problem may be?
Or how to troubleshoot it further ?

My guess is its the 15 yr old control board up in the attic unit (mod# 321257-401). I replaced the control board in the other zone/basement unit a year ago although that was an issue with the heat and I was getting an LED error code. Tested the heat on the attic unit today and it appears to be working fine. No LED codes are showing up on it either. So I hate to spend $150 to replace it if that's not it.

thanks in advance!

Use a multi meter and see if the contactor is getting enough voltage. Might only be getting 18 volts. Instead of 24 to 27.

Thanks beenthere for the quick response - Without line voltage it's a steady 25.7v; when I apply the line voltage it stays at 25.7 until it starts chattering and then of course it varies (although mostly showed minimal drop/ ~24v, but I guess that's because the digital meter doesn't react quick enough?)

Could it be a problem with the HPC or LPC ?

Its possible.

anyway to test/diagnose?

Ohm them out. Should be zero resistance.

checked resistance - zero across both HPC and LPC.
Any other ideas ?

Possible soild state compressor time delay that's tied right into the low voltage side. Try .turn off condenser line voltage. take wires off time delay.. turn power back on check for chatter.. Good Luck.